This invention relates to an oil type damper for braking and absorbing the opening and closing motion of, for example, a freely openable lid having one end thereof pivotally attached to some type of mechanical device, and more particularly to an improved oil type damper of a construction such that otherwise possible leakage of the damper oil due to a change in ambient temperature can be prevented and, at the same time, the work of filling the damper with oil can be carried out with ease.
In an electric device such as a cassette tape recorder or a video tape recorder, a cassette tape as a recording medium is set in place in the cassette holder of the device proper and set running therein to effect desired recording or playback. In this case, the cassette holder itself is popped out of the device proper by pressing an ejection button or the lid for the cassette holder is caused to fly open to permit the cassette to be removed from or inserted into the cassette holder. Thereafter, the cassette holder or the lid is pushed back into place on the device proper to ready the device for use. The vibration attendant upon the opening and closing motion of the cassette holder or the lid has an adverse effect upon the device. Further, the impact causes a disagreeable sensation to the hand of the person handling the device. To overcome these disadvantages, dampers of various forms have been proposed to date. Broadly, these dampers may be divided into frictional dampers and oil type dampers. The dampers of the frictional type suffer a gradual decline in performance with use. They cannot maintain good braking performance and have poor durability. Frictional dampers have therefore given way to the oil type dampers because the drawbacks of such dampers as described above are inherent to the structure of these dampers and can be eliminated only to a limited extent. This does not mean that the oil type dampers are perfectly free from disadvantages. When the ambient temperature changes, for example, there is the possibility that the housing filled with the oil will permit leakage of oil, which could result in complete impairment of the damper's function.
In Japanese Utility Model Application Disclosure SHO 58(1983)-189843, the inventors of this invention propose an oil type damper which is provided in a housing thereof with a soft flexible membrane possessing elasticity as well as a rotator so that any thermal expansion of the oil in the housing will be absorbed by the flexible membrane and consequently prevented from leaking out of the housing. Generally in any of the conventional oil type dampers including the oil type damper proposed by the inventors as described above, the braking disk of the rotator is coated on the opposite surfaces and the circumferential boundary thereof with oil such as silicone grease with the aid of a brush before it is set in place inside the housing during the course of assembly of the damper. The work of applying the oil to the braking disk calls for the most meticulous care. Highly advanced skill on the part of the worker is indispensable to uniform application of a stated amount of oil to the interior of the housing.